1. Field of the Invention
The present invention relates to a novel polypeptide, a polynucleotide coding for said polypeptide, a recombinant plasmid DNA into which said polynucleotide has been inserted, a host cell transformed with said recombinant plasmid DNA, a process for preparing said polypeptide or polynucleotide comprising isolating the polypeptide or polynucleotide from a culture of said host cells, a process for screening for a substance that modulates the activity of said polypeptide and a kit for said screening, a process for screening for a substance that modulates the expression of said polypeptide or polynucleotide and a kit for said screening, a process for screening for a substance that binds to said polypeptide and a kit for said screening, a process for detecting the activity of said polypeptide and a kit for said detecting, a process for detecting the expression of said polypeptide or polynucleotide and a kit for said detecting, an antibody that specifically binds to said polypeptide, an active fragment thereof, a chimeric antibody thereof, and a humanized antibody thereof, a pharmaceutical composition consisting of said human antibody or a single strand antibody thereof, and a pharmaceutical composition consisting of said polypeptide.
2. Background Art
2′,5′-oligoadenylate (hereinafter referred to as “2-5A”) is an oligoribonucleotide in which two or more adenosines have been phosphodiester-bound between their 2′- and 5′-positions, and a triphosphate has been bound at the 5′-position of the 5′-terminal adenosine. 2-5A functions as a modulator molecule within a cell, and the system for control of cellular or viral proliferation mediated via RNA degradation by 2-5A is called the 2-5A system (M. R. Player and P. F. Torrence, “The 2-5A system: modulation of viral and cellular processes through acceleration of RNA degradation,” Pharmacology & Therapeutics, published in Great Britain in 1998, vol. 78, pp. 55-113).
The 2-5A system involves three enzymes. The first 2-5A synthetase, which is a 2-5A synthesizing enzyme is activated by double-stranded RNA; 2-5A is synthesized from ATP by 2-5A synthetase. Secondly 2′,5′-oligoadenylate phosphodiesterase (2′,5′-oligoadenylate phosphodiesterase; hereinafter referred to as “2′-PDE”), which is an enzyme that degrades 2-5A into AMP and ATP. Thirdly RNase L, which is a 2-5A dependent ribonuclease activated by 2-5A. Activated RNase L degrades single stranded RNA, such as mRNA, and as a result, inhibits protein syntheses and cell proliferation. It is believed that in the 2-5A system, the amount of 2-5A present is important, and that the activity of RNase L is modulated by the balance between the synthesis and degradation of 2-5A.
The 2-5A system has been well investigated as one of the mechanisms of the anti-viral activity of interferon. Interferon is a cytokine which induces 2-5A synthetase in a manner mediated by the cell membrane. Since many viruses have a double-stranded RNA form during the process of infection and proliferation, and 2-5A synthetase is activated by double-stranded RNA, 2-5A synthetase is preferentially activated in a cell infected with a virus. It is believed that the 2-5A level in a cell that has been infected with a virus is elevated by activated 2-5A synthetase, this is accompanied by the activation of RNase L, and inhibition of protein synthesis in the virus-infected cell, leading to inhibition of viral proliferation. Direct viral RNA degradation by activated RNase L and the resulting inhibition of viral proliferation are also known to occur.
Interferon is a multi-functional molecule that has, in addition to anti-viral action, various biological activities such as a cell proliferation suppression effect, an anti-tumor effect, activation of macrophage, enhancement of the activity of natural killer cells, immune response modulation action, a negative feedback action on osteoclast differentiation, modulation of the induction of differentiation etc. (Kohei Miyazono and Kazuo Sugamura eds., “Bio Science Yogo Library, Cytokines and Growth Factors,” published by Youdosha Co., Ltd. Japan, 1998, pp. 178-185; H. Takayanagi et al., “RANKL maintains bone homeostasis through c-Fos-dependent induction of interferon-β,” Nature, published in Great Britain in 2002, vol. 416, pp. 744-749).
Mutations in the RNase L gene were observed among prostate cancer-developing families (J. Carpten et al., “Germ line mutations in the ribonulease L gene in families showing linkage with HPC1,” Nature Genetics, published in the United States in 2002, vol. 30, pp. 181-184). Further, it has been suggested that 2-5A synthetase is induced by nerve growth factor (M. Saarma et al., “Nerve growth factor induces changes in (2′-5′) oligo(A) synthetase and 2′-phosphodiesterase activities during differentiation of PC12 pheochromocytoma cells,” Experimental Cell Research, published in Sweden in 1986, vol. 166, pp. 229-236), and thus the 2-5A system may be involved in expression of functions of cytokines other than interferon. In addition, it has been suggested that in the process of osteoclast differentiation, interferon inhibits differentiation by a negative feedback mechanism (H. Takayanagi et al., “RANKL maintains bone homeostasis through c-Fos-dependent induction of interferon-β,” Nature, published in Great Britain in 2002, vol. 416, pp. 744-749).
A 2′-PDE inhibitory substance may exert anti-viral, anti-tumor, and immuno-activating actions via the 2-5A system by elevating 2-5A levels in vivo or in a cell. However, to date, studies on 2′-PDE have been limited. Polypeptides having 2′-PDE activity purified from mouse and bovine sources are known. Polypeptides purified from two types of cell derived from mice had a molecular weight of 35,000 determined by SDS-polyacrylamide gel electrophoresis and an apparent molecular weight of 40,000 determined by gel filtration chromatography; these polypeptides hydrolysed 2′,5′-oligoadenylate to an extent similar to or greater than the extent to which they hydrolysed 3′,5′-oligoadenylate; and had the activity of degrading the C-C-A terminus of tRNA (A. Schmidt et al., “An interferon-induced phosphodiesterase degrading (2′-5′) oligoadenylate and the C-C-A terminus of tRNA,” Proceedings of National Academy of Science, U.S.A, published in the United States in 1979, vol. 76, no. 10, pp. 4788-4792). The polypeptide purified from a bovine source had a molecular weight of 65,000 determined by SDS-polyacrylamide gel electrophoresis, an apparent molecular weight of 56,000±11,000 determined by gel filtration chromatography and an isoelectric point of around pH 8.3, but its ability to hydrolyse 2′,5′-oligoadenylate was about one hundredth of its ability to hydrolyse 3′,5′-oligoadenylate (W. G. Hearl, Purification and Characterization of a 2′-Phosphodiesterase from Bovine Spleen,” Journal of Biological Chemistry, published in the United States in 1987, vol. 262, no. 17, pp. 8377-8382). Thus, it was not clearly established that the polypeptide was a 2′-PDE.